This invention relates to devices for feeding workpieces one at a time from a stack, and more particularly to the feeding of workpieces, such as letter mail or other non-uniform sheet-like articles on which some operation is to be performed. The field of art to which the invention most likely pertains is located in a class of devices generally relating to sheet feeding or delivering. Class 271, U.S. Patent Office Classification, may be the applicable general area of art in which the claimed subject matter of the type involved here may be classified.
Examples of prior devices in the arts to which this invention most likey pertains are disclosed in U.S. Pat. Nos. 3,186,708, 3,108,801, 3,103,355, 3,048,393, 3,025,051 and 2,856,187.
In feeding workpieces from a stack, when the workpieces are uniform in size and surface condition and of substantially the same length in the direction of feed, suitable timing mechanism such as disclosed in U.S. Pat. Nos. 2,973,202 and 3,264,630 may be provided to move workpieces forward in an orderly fashion for processing. However, where the workpieces are of varying length in the direction of feed and of varying surface conditions, such as in the processing of letter mail, those types of control mechanisms will not operate effectively. The longer workpieces will overlap in the flow from the stack or several workpieces will stick together, and the controls will not adjust to these changing conditions, causing too frequent interruption in the operation of the feed system.
The prior art devices which deal with removing workpieces of non-uniform size from a stack of mail or the like are generally incapable of separating doubles once taken from the stack. Whatever is pulled from the stack is fed through the device and those pieces of mail hidden behind other pieces either cause a stoppage or are not detected and properly processed.